Awwww hun, try not to think the worst, not easy I know but please don't be hard on yourself about this.
If you need to go, then try to relax and let it happen. Constipation is common in first tri anyways, so by tensing up you will only make yourself feel worse.
Maybe try eating plenty of fibre foods in your diet and taking something like Lactulose or Fibogel to help soften things up and get it moving.
I know sometimes straining to go can cause a bit of bleeding from the bottom but thats not to say it will lead to a MC. I am not aware that having a poo causes that to happen.
Many of us get stuck and can't poo in the early weeks. I found it painful to go but managed in the end. Of course its not pleasant and it blooming hurt me a few times I can recall, but better out than in when it has to happen.
I'd go buy some over the counter Fibogel, take it, drink plenty of water regularly also, have a nice walk to help things along, soak in a warm bath and when you feel the need, just relax and let it happen. Don't force it, but just try to relax. Listen to some music or something to distract you if need be. Even if you have to sit there 20 minutes, or get off and walk around before trying again. Raising your knees up off the floor (a small box is good to put your feet on) helps when needing a #2 as it makes it easier to pass.
I think once you go the first time it'll be a big mental barrier passed and you'll feel more comfortable in all ways.
Hope that was of some help
